Berlin (dpa) — The basic design of power and garden tools hasn’t changed much over the years — a lawn mower is still a lawn mower. What has changed is the batteries that power them. They have now become so long-lasting that they challenge petrol and mains-powered devices. The reason is lithium-ion batteries. They can store a large amount of energy while remaining small and light. It also helps that manufacturers now use a standardised and therefore replaceable battery system for their devices. That means that the same rechargeable battery fits equally well in the hedge trimmers, lawn mowers, c…